A subcategory is the grouping node beneath a driver type, the browse-page heading a reader sees above a cluster of entities that share a primary branch, such as the Ethics subcategory under Philosophers or under Works. Subcategory entities exist so each grouping has a real address to carry prose, an emblem anchor and a stable slug, computed from the live membership rather than invented by hand. This category excludes the sub group label a reader sees inside a subcategory listing, which carries no page of its own and hangs its facts off the parent subcategory instead.